1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device, which has the step of forming a buried type copper-based metal interconnection.
2. Description of the Related Art
In the formation of a semiconductor integrated circuit such as an ULSI for which progress to attain further miniaturization and more densely spaced arrangement has been gathering more speed, copper is a particularly useful material of the electrical connection for forming the interconnection of good performance and high reliability, because of its low electrical resistance and high resistance against the electromigration and the stress migration.
Since it is difficult to work copper into shape by means of dry etching, a copper interconnection is currently formed by so-called damascene method, for instance, in the following way.
Firstly, a sunken section such as a trench or a connection hole is formed in an insulating film formed on a silicon substrate. Next, after a barrier metal film is formed on the surface inclusive of the inside of this sunken section, a copper film is grown by the plating method so as to fill up this sunken section. Polishing is then carried out by the chemical mechanical polishing (referred to as “CMP” hereinafter) method until the surface of the insulating film other than the sunken section is completely exposed, so that the surface may be planarized. Thereby, the formation of an electrical connection section such as a buried copper interconnection, a via plug or a contact plug, which is made of copper filling the sunken section with a barrier metal film lying therebetween, is accomplished.
For the CMP slurry used in the formation of a copper interconnection of this sort, a slurry which contains an oxidizing agent and a polishing material as the main components and further comprises an organic acid such as an amino acid or a carboxylic acid, is generally used.
For example, in Japanese Patent Application Laid-open No. 233485/1995, there is disclosed a polishing agent for a copper-based metal which contains an oxidizing agent (hydrogen peroxide), polishing grains, water and at least one type of an organic acid selected from the group consisting of aminoacetic acid (glycine) and amidosulfuric acid. Further, it is described therein that, with such a polishing agent being used, through the oxidation effect of the afore-mentioned oxidizing agent, an oxide layer is formed, on the surface of copper or copper alloy, to serve as an etching barrier, while this copper or copper alloy is immersed in the agent, and in polishing copper or copper alloy, the removal of the afore-mentioned oxide layer is made mechanically, and the afore-mentioned organic acid facilitates to etch the exposed copper or copper alloy.
Further, in Japanese Patent Application Laid-open No. 83780/1996, there are disclosed a polishing agent which contains an oxidizing agent (hydrogen peroxide), water, benzotriazole or its derivative, a polishing agent containing polishing grains and aminoacetic acid (glycine) and/or amidosulfuric acid; and a polishing method wherein a CMP is carried out using this polishing agent to form a film of copper or copper alloy within a sunken section of a substrate. Further, it is described therein that, by performing the CMP with this polishing agent, a protective film is formed on the film that is to be polished so as to prevent the isotropic chemical etching from occurring, and then the removal of this protective film is made, by mechanical polishing, on the surface of the raised section of the film for polishing, and, thereby, a conductive film of high reliability with little dishing or damage can be formed.
Further, in Japanese Patent Application Laid-open No. 238709/1999, there is disclosed a CMP slurry for copper polishing, which contains citrate, an oxidizing agent (hydrogen peroxide), a polishing material and 1,2,4-triazole or benzotriazole. Further, it is described therein that the use of the CMP slurry can improve the removing rate of copper and the addition of the afore-mentioned triazole or benzotriazole can raise the planarity of the copper layer.
In recent years, as the semiconductor integrated circuit has been increasingly miniaturized and its arrangement, more densely spaced, the increase in interconnection resistance and further complication of the logic circuits which result from the miniaturization of the interconnection have become problems to be coped with, and the employment of the multi-layered interconnection which can reduce the interconnection length has become more and more spreading. Accompanying the increase in the number of layers through the employment of the multi-layered interconnection structure, however, the unevenness of the substrate surface grows and the difference in level widens. The enlargement of the difference in level, owing to the employment of the multi-layered structure may cause various problems including the short-circuited interconnection and the leakage of current, both of which may be brought about by metal residues left in the sunken section of the upper layer(s) after the CMP, and the focus shift in the step of lithography. Therefore, it is essential for the slurry not to create substantial dishing (in other words, to provide a high planarity). Further, in the multi-layered interconnection, the top layer section of the interconnection is used for the interconnection for power supply, the interconnection for signal or the interconnection for clock, and for the sake of lowering these interconnection resistances to reduce the voltage change and improve various characteristics, it is required to make the interconnection trench deep and form thick interconnections. In such a case as a thick copper film is formed and, then, a copper interconnection is formed, the polishing amount of copper which is to be removed in the step of one CMP increases and, thus, the time required for the step of polishing becomes considerably long, giving rise to a problem of lowering the throughput. As a result, copper polishing at a higher polishing rate is strongly demanded.
In general, in order to polish copper at a high polishing rate, the amounts of components for copper etching such as the oxidizing agent and the acid, which are contained in the polishing slurry, are made higher to raise their chemical effects. However, if the chemical effects of the polishing slurry are too strong, even the copper formed as the buried section may be etched to create a hollow (dishing), and the reliability for the electrical connection section such as the interconnection and the via plug may fall.
Further, with the intention of suppressing dishing in the copper interconnection or the like, if the content of the dishing inhibitor such as benzotriazole or 1,2,4-triazole is made too high, the polishing rate (the removing rate) of copper may drop a great deal. Further, there become liable to arise problems that polishing may generate strong vibrations and that, in a state where the barrier metal film is exposed, the interconnection edge damage may grow with the exposed section of the barrier metal film being the starting point.
It is, therefore, difficult to polish copper at a high polishing rate, and, at the same time, prevent the dishing from occurring satisfactorily.